1. Field of the Invention
The present invention relates generally to the field of molecular biology, stem cells and differentiated cells. More particularly, it concerns differentiation programming or reprogramming of somatic cells and undifferentiated cells.
2. Description of Related Art
In general, stem cells are undifferentiated cells which can give rise to a succession of mature functional cells. For example, a hematopoietic stem cell may give rise to any of the different types of terminally differentiated blood cells. Embryonic stem (ES) cells are derived from the embryo and are pluripotent, thus possessing the capability of developing into any organ or tissue type or, at least potentially, into a complete embryo.
Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inserting certain genes. Induced pluripotent stem cells are believed to be identical to natural pluripotent stem cells, such as embryonic stem cells in many respects, such as in terms of the expression of certain stem cell genes and proteins, chromatin methylation patterns, doubling time, embryoid body formation, teratoma formation, viable chimera formation, and potency and differentiability, but the full extent of their relation to natural pluripotent stem cells is still being assessed.
IPS cells were first produced in 2006 (Takahashi et al., 2006) from mouse cells and in 2007 from human cells (Takahashi et al., 2007; Yu et al, 2007). This has been cited as an important advancement in stem cell research, as it may allow researchers to obtain pluripotent stem cells, which are important in research and potentially have therapeutic uses, without the controversial use of embryos.
However, at this stage in the study of these induced pluripotent stem (iPS) cells, researchers are using integrating viral plasmids, which insert the genes into the genome of target cells, potentially introducing mutations at the insertion site. Therefore, there is a need to develop a method to induce pluripotent stem cells essentially free of exogenous viral components.
Due to the significant medical potential of cell therapy and tissue transplantation, there also exists an urgent need for the production of any desired cell types by altering cellular differentiation status of an available cell population. Each specialized cell type in an organism expresses a subset of all the genes that constitute the genome of that species. Each cell type is defined by its particular pattern of regulated gene expression. Cell differentiation is thus a transition of a cell from one cell type to another and it involves a switch from one pattern of gene expression to another. Cellular differentiation during development can be understood as the result of a gene regulatory network. A regulatory gene and its cis-regulatory modules are nodes in a gene regulatory network; they receive input and create output elsewhere in the network. The similar mechanisms may also apply to dedifferentiation, for example, inducing pluripotency from somatic cells as mentioned above, and transdifferentiation, specifically referring to transformation of one differentiated cell type into another. Transcription factors controlling the development choices have been studied to change differentiation status; however, viral vectors have also been widely used. Therefore, there is a need for improved viral free differentiation programming methods.